Method and apparatus for controlling consistency



Ma h 19, 68 L. v. FEGAN, JR., ETAL 7 METHOD AND APPARATUS FOR CONTROLLING CONSISTENCY Filed Feb' 24, 1966 WATER SUPPLY 2 {22 VCONDUCTIVITY CONTROLLER I METER RECORDER 20 SUPPLY INV EN TOR S l4 l6 1 Lloyd l4 Fegan Jr.

Amab/eE. Ema/2d United States Patent 3,373,944 METHOD AND APPARATUS FOR CONTROLLING CONSISTENCY Lloyd V. Fegan', Jr., Lebanon, and Amable E. Emond, Reading, Pa., assignors to Bethlehem Steel Corporation, a corporation of Delaware Filed Feb. 24, 1966, Ser. No. 529,820 8 Claims. (Cl. 241-15) This invention relates generally to method and apparatus for continuously and automatically measuring and controlling the consistency of a stream of material. More specifically, this invention relates to method and apparatus for continuously and automatically maintaining at a desired value the consistency of a mixture of solids and water in a grinding mill.

Conventionally, ores from which metal values such as iron, copper, etc., are to be recovered are first reduced in particle size in grinding mills such as the well known rod mil-l. As is known to those familiar with this art, a mixture of ore and water is introduced into the rod mill and subjected to the action of rods therein. The mixture in the rod mill should not be too thin, as otherwise the rods will abrade each other, causing excessive wear of the rods and requiring frequent replacement thereof with consequent down-time of the ,rod mill. Also, the mixture in the rod mill should not be too thick or stiff, as otherwise the ore will not effectively be reduced in particle size. Ideally, the consistency of the mixture of comminuted ore and water at the rod mill discharge should be of such value that the mixture in ore density. By way of illustration, the specific gravity of magnetite is about twice that of rock.

There may be variations in the richness of ores fed to a continuously operating rod mill. In many instances, to obtain a rod mill discharge of the desiredconsistency, the percentage of solids in the rod mill discharge may range all the way between 70% and 85%. This range may even be wider in other instances. With this in mind, it will be appreciated that measurement and control of the consistency of the rod mill discharge is not a simple problem. I

One of the objects of this invention is to provide method and apparatus for continuously and automatically measuring and controlling the consistency of a stream of material.

Another of the objects of this invention is to provide method and apparatus for continuously and automatically measuring and controlling the consistency of a mixture of solids and water in a grinding mill.

A specific object of this invention is to provide method and apparatus based upon the electrical conductivity of a mixture of solids and water discharged from a grinding mill for continuously and automatically measuring and controlling the consistency of such mixture in the grinding mill.

A more specific object of this invention is to provide method and apparatus for continuously and automatically measuring the consistency of a mixture of solids and water discharged from a grinding mil-l as a function of the electrical conductivity of such mixture and for continuously and automatically maintaining at a desired value the consistency of such mixture within the grinding mill by regulating the amount of water introduced into the grinding mill with the aforementioned solids.

Other and further objects of this invention will become apparent during the course of the following description and by reference to the appended claims and to the accompanying drawing.

Briefly, it has been discovered that the foregoing objects can be attained by continuously passing an electrical current through spaced electrodes in a conduit or trough receiving the grinding mill discharge and measuring the depth of the mixture of solids and water in said conduit or trough in terms of electrical conductivity, and automatically operating a control valve in a water line leading to the grinding mill in response to the electrical conductivity of the mixture in the conduit or trough.

Referring now to the drawing in which like numerals represent like parts in the several views:

FIGURE 1 represents diagrammatically and partially in elevation a grinding mill of the type known as a rod" mill with the means of the present invention associated therewith for regulating the consistency of the contents of the rod mill together with other equipment to establish the environment of the rod mill but not essential to the present invention.

FIGURE 2 represents an enlarged view in elevation of the discharge end of the rod mill with the conduit receiving the mixture of comminuted solids and water, showing the spaced electrodes for measuring the depth of the mixture in the conduit in terms of conductivity, and partially broken away to show the taper of the linings therein.

FIGURE 3 represents an enlarged section taken along the line 33 of FIGURE 2.

A typical grinding circuit is seen in FIGURE 1 as comprising a rod mill 1 for initial comminution of solids and a ball mill 2 for further comminution of solids. Hopper 3 at the inlet end of rod mill 1 receives solid feed from conveyor 4 and water from line 5 for introduction into the said rod mill. Inclined conduit 6 communicates between sump 7 collecting the discharge from rod mill 1 and the inlet end of ball mill 2. Sump 8 receives the discharge from ball mill 2. It will be understood that other elements of machinery and the like, conventionally employed in systems of this type, may be included in the illustrated arrangement although the same are not specifically shown.

The arrangement of apparatus thus far described is conventional. I

Conduit 6 includes a section 9 preferably of the same cross section and held in place by means of bolted flanges 10. A liner 11, of abrasion-resistant electrically insulating material, is mounted within the said section 9, extending completely around the inner periphery thereof, and the two ends of the liner 11 preferably are tapered. Additionally, a second liner 12, also of abrasion-resistant electrically insulating material, is mounted within the said section 9 adjacent liner 11, and preferablyextends only around the lower half of the said liner 11. The two ends of liner 12 as well as the longitudinal edges thereof preferably are tapered.

Electrodes 13 are spaced from each other longitudinally of section 9 and extend through the said section 9 and liners 11 and 12 at the bottoms thereof. Electrodes 13 are provided with electrically insulating bushings 14 separating the same from the metallic wall of section 9 thereby to avoid short circuting, and the innermost portions of the said electrodes 13 (i.e., those portions which are in electrical communication with the contents of section 9) are provided with enlarged faces 15 of abrasion-resistant electrically conductive material such as tungsten carbide mounted flush with the inner wall of liner 12.

Electrical leads 16 communicate between electrodes 13 and conductivity) meter 17 (sometimes referred to as moisture meter). Conductivity meter 17 is the Wheatstone bridge type, one of the resistances of the bridge being the resistance of the path between electrodes 13 in section 9. An alternating current is passed between electrodes 13, and the conductivity meter 17 produces an electrical output which is a function of the resistance (or conductivity) of the electrical path between said electrodes 13. Preferably, conductivity meter 17 is of the type disclosed in my co-pending application Ser. No. 418,814 filed Dec. 16, 1964, and entitled Method and Apparatus for Measurement and Control of Moisture.

The electrical output of conductivity meter 17 is communicated through electrical leads 18 to a controller recorder 18. Controller recorder 19 is a standard pneumatic controller recorder device having an electrical input (connected in this case to electrical leads 18) and a pneumatic input (connected in this case to air line 20 communicating with a source 21 of compressed air). Controller recorder 19 produces a pneumatic signal or output in response to the electrical input thereto through electrical leads 18.

The pneumatic output of controller recorder 19 is communicated through line 22 to the diaphragm of control valve 23 in water line 5, thereby regulating the flow of water from a source 24 of water through line to hopper 3.

With the grinding circuit in operation, solids from conveyor 4 and a certain amount of water from line 5 are continuously introduced into hopper 3 of continuously operating rod mill 1. The mixture of comminuted solids and water passes from rod mill 1 to sump 7 and enters conduit 6. Section 9 of conduit 6 is of such size relative to the maximum rate of fiow therethrough of the mixture of comminuted solids and water that the said section 9 is never completely filled therewith. In other words, the level of the mixture of comminuted solids and water will always vary with the rate of flow of said mixture through section 9. Thus, for illustrative purposes only and exaggerated for clarity, the level of the mixture in section 9 may vary between 25 and 26 (referring to FIGURE 3), corresponding respectively with relatively low rates of flow of stitf mixtures and with relatively high rates of flow of thin mixtures. Stiff mixtures, of course, have less water content than thin mixtures. The cross-section of section 9 may vary from one application of the present invention to another, and section 9 may even be an open trough, so long as variations in the level of the mixture therein are permitted to occur. Electrodes 13 are preferably always below the minimum level of the mixture in section 9 (i.e., electrodes 13 are always covered by the mixture of comminuted solids and water).

It will be noted that the cross sectional area of the bed of the mixture in section 9, as shown in FIGURE 3, with level 25 is greater than with level 26. It will be apparent from this fact that the conductivity of the mixture in sec tion 9 as measured by electrodes 13 will be greater for stiff mixtures having level 25 than for thin mixtures having level 26.

There will be a level of mixture in section 9 corresponding with the optimum consistency of said mixture, provided the rate at which solids are fed into rod mill 1 remains constant. Variations in mixture level from that level corresponding with optimum consistency will be sensed by conductivity meter 17 which will control the setting of control valve 23 through controller recorder 19. When the level of mixture in section 9 falls below the optimum level, the rate at which water is introduced into rod mill 1 will be decreased to stiifen the mixture to the desired optimum consistency. Conversely, when the level of mixture in section 9 rises above the optimum level, the rate at which water is introduced into rod mill 1 will be increased to thin the mixture to the desired optimum consistency. It will be recognized that this is a form of closed loop control.

Moisture meters employing probes to measure moisture content by the resistivity (or conductivity) of material between the probes or electrodes are old, and no attempt is being made to cover such conventional apparatus in this application. However, such conventional apparatus has always been used on constant depth beds of material under test and never on material beds having depth fluctuating with fluctuations in consistency and moisture content. It should be understood that the present invention operates on mixtures of solids and water of such thickness that fluctuations in the consistency thereof will cause corresponding fluctuations in the depth of the bed in section 9.

Grinding circuits employing the foregoing invention have worked quite successfully with rod mill mixtures having 70-85% solids (magnetite, pyrites and rock).

Electrodes 13, while shown as spaced longitudinally in section 9, may also be disposed other than longitudinally relative to each other. For instance, electrodes 13 may be spaced from each other transversely of section 9. If a rectangular conduit or trough is employed, it may be desired to install electrodes 13 in the lower portions of the side Walls, so long as the said electrodes 13 are at all times covered by the mixtures being measured.

As previously mentioned, the cross-section of section 9 may vary from one application of the present invention to another. The degree of resolution of the electrical readings in relation to fluctuations in the depth of the mixture in section 9 can be fixed or predetermined and made uniform or non-uniform (logarithmic, etc.) as desired by selecting a suitable cross-section for section 9. Thus, the circular cross-section of section 9 as shown in FIGURE 3 may, if desired, be replaced by a rectangular crosssection, a V cross section, an erect or inverted delta crosssection, or curvilinear cross-sections such as parabolas, etc., in order to suit the requirements of a particular operation.

We claim:

1. Apparatus for controlling the consistency of an electrically conductive mixture flowing as a bed through an inclined conduit, said mixture including solids and a liquid added to said solids by means of a liquid line having a valve therein, the depth of the bed increasing above a predetermined value when the consistency of said mixture increases above a predetermined value and decreasing below the predetermined value when the consistency of the mixture decreases below the predetermined value, said apparatus comprising:

(a) a pair of spaced electrodes associated with said conduit and adapted to electrically contact said mixture in said conduit,

(b) means for passing an electrical current through said electrodes and through the bed of said mixture between said electrodes, said means measuring the electrical resistance of said bed of said mixture between said electrodes and producing a signal varying with variations in the depth of the bed of said mixture between said electrodes,

(c) a liquid line adapted to add liquid to said solids,

(d) a valve in said liquid line,

(e) means placing said signal in operative relationship to said valve to control said valve to increase the flow of liquid therethrough to the conduit when the depth of the bed of mixture between said electrodes increases .above a predetermined value and alternatively to decrease the flow of liquid therethrough to the conduit when the depth of the bed of mixture between said electrodes decreases below the predetermined value.

2. Apparatus as in claim 1, further comprising:

(if) said spaced electrodes being mounted in a wall of said conduit adjacent the lower portion thereof substantially flush with the inside thereof, said electrodes being electrically insulated from said conduit.

6 3. Apparatus as in claim 1, further comprising: liquid continuously being added to said solids, said method (f) the cross-sectional area of said conduit transverse comprising:

to the flow therein of said bed always being greater (a) forming a moving stream of said mixture, said than the cross-sectional area of said bed transverse to stream having a depth varying directly with variathe direction of flow. 5 tions in the consistency of said mixture, there being 4. In association with a continuously operating grinda predetermined depth of stream corresponding with ing mill having an outlet end, said grinding mill continuthe desired value of consistency, ously receiving an electrically conductive mixture of solids (b) measuring the resistance of said mixture in a porand water and continuously discharging said mixture from n of said st eam by passing an electrical current said outlet end, apparatus for continuously controlling 10 between two'fixed spaced Stations in Said Stream and the consistency of said mixture within said grinding mill, through the IniXt-ufe between the two Said Stations, said apparatus comprising: (0) regulating the flow of liquid to said solids to in- (a) an inclined conduit adapted t o ti l crease the flow of liquid when the resistance of said eiv the mixtu e f lid d Water di h d fr mixture between the two stations decreases below a the outlet end of said grinding mill, said conduit being predetermined Value Corresponding t0 an increase in further adapted to continuously form therein a bed of the depth of Said Stream above a predetermined V l id i t flo i l i i ll through said com and alternatively to decrease the flow of liquid when duit, the depth of said bed increasing above a predethe resistance of said mixture between the two staj d value h the consistency f Said mixture tions increases above the predetermined value correin said grinding mill increases above a predetermined Spending to a decrease in the depth of Said Stream value and decreasing below the predetermined value below the predetermined Valueh the Consistency f the mixture in said grind-ing 8. Method for contmuously controlling and maintainmfll decreases below the predetermined value, mg at a desired value the consistency of an electrically (b) a pair f spaced electrodes associated with Said conductive mixture of solids and water within a continuconduit and adapted to electrically contact said mixously operatmg grindmg min, Said method Comprising: turein i Conduit, (a) forming a moving stream of said mixture as the (c) means for passing an electrical current through said same 15 dlscharged from the grinding mill, Said electrodes and through the bed of said mixture bei i having a.depth varying directly with variatween said electrodes, said means measuring the elec- Hons m the .conslstency of Said mixture there being trical resistance of said mixture between said eleca Predqtermmed depth Stream cor responding with trodes and producing a Sign a1 varying with variations the desired value of consistency in sa1d grinding mill,

in the depth of the bed of said mixture between the measuripg the resistance 9 Said mixture in por- Said electrodes, tron of said stream by passing an electrical current (d) a valve controlling the flow of water into Said between two fixed spaced stations in said stream and g g mill through the mixture between the two said stations,

(e) means placing said signal in operative relationship (c) rfggulatmg the flow of Water to said grmding min to said valve to control said valve to increase the to-mcricase the flow of Water n the resistance of flow of water therethrough to said grinding mill when said mixture between the two stamens iiecreases be the depth of the bed of said mixture between the low a Predetermmed yal-ue correspondmg to an in spaced electrodes increases above a predetermined criease m the depth of Sam-1 Stream above a predetervalue and alternatively to decrease the flow of water mmed Value and altqmatlvely to. deciease the flow therethrough to said g g mill when the depth of water when the reslstance of sa1d mixture between of the bed of said mixture between the spaced electhe two stations Increases above predetermmed trodes decreases below the predetermined value. Vailue correspondmg to a decrease In the depth of 5. Apparatus as in claim further comprising: said stream below the predetermined value.

(f) said spaced electrodes being mounted in a wall of said conduit adjacent the lower portion thereof substantially flush with the inside thereof, said elec- UNITED STATES PATENTS References Cited trodes being electrically insulated from said conduit. ,78 ,948 3/1957 Hage 24134 6. Apparatus as in claim 4, further comprising: 2,833, 82 5/1 58 Weston 24l3O (f) the cross-sectional area of said conduit transverse 2,965,316 12/1960 HeHderSOn 24134 t0 the flow therein of said bed always being greater ,1 ,2 /19 Masuda 241-16 than the cross-sectional area of said bed transverse 3,248,061 4/1966 Franz 241-30 to the direction of flow of said bed. 55 3,255,975 6/1966 Malin 24134 7. Method for continuously controlling and maintain- 3,282,514 11/1966 Putz 2 41 33 X ing at a desired value the consistency of an electrically conductive mixture, said mixture including solids and a HARRISON L. HINSON, Primary Examiner. 

7. METHOD FOR CONTINUOUSLY CONTROLLING AND MAINTAINING AT A DESIRED VALUE THE CONSISTENCY OF AN ELECTRICALLY CONDUCTIVE MIXTURE, SAID MIXTURE INCLUDING SOLIDS AND A LIQUID CONTINUOUSLY BEING ADDED TO SAID SOLIDS, SAID METHOD COMPRISING: (A) FORMING A MOVING STREAM OF SAID MIXTURE, SAID STREAM HAVING A DEPTH VARYING DIRECTLY WITH VARIATIONS IN THE CONSISTENCY OF SAID MIXTURE, THERE BEING A PREDETERMINED DEPTH OF STREAM CORRESPONDING WITH THE DESIRED VALUE OF CONSISTENCY, (B) MEASURING THE RESISTANCE OF SAID MIXTURE IN A PORTION OF SAID STREAM BY PASSING AN ELECTRICAL CURRENT BETWEEN TWO FIXED SPACED STATIONS IN SAID STREAM AND THROUGH THE MIXTURE BETWEEN THE TWO SAID STATIONS, (C) REGULATING THE FLOW OF LIQUID TO SAID SOLIDS TO INCREASE THE FLOW OF LIQUID WHEN THE RESISTANCE OF SAID MIXTURE BETWEEN THE TWO STATIONS DECREASES BELOW A PREDETERMINED VALUE CORRESPONDING TO AN INCREASE IN THE DEPTH OF SAID STREAM ABOVE A PREDETERMINED VALUE AND ALTERNATIVELY TO DECREASE THE FLOW OF LIQUID WHEN THE RESISTANCE OF SAID MIXTURE BETWEEN THE TWO STATIONS INCREASES ABOVE THE PREDETERMINED VALUE CORRESPONDING TO A DECREASE IN THE DEPTH OF SAID STREAM BELOW THE PREDETERMINED VALUE. 